found the following passage in some sweepstakes official rules

Sponsor reserves the right to verify eligibility qualifications of any winner. If a Canadian resident wins a prize, that person must also answer correctly within a 5 minute time period a mathematical skill-testing question without the benefit of any human, mechanical or electronic calculating devices before the prize will be awarded. It is the sole responsibility of the entrant to notify the Sponsor in writing if the entrant changes his or her email address. To do so, email  sweepstakes@bizrate.com and type "Sweeps Address change" in the subject line.